Communication services such as voice calls have traditionally been provided via circuit switched (CS) networks, such as the Public Switched Telephone Network (PSTN) or cellular wireless networks. Over the last several years, new means of providing communication services over IP networks have emerged, commonly referred to as Voice over IP (VoIP). A prevalent protocol used to implement VoIP is the Session Initiation Protocol (SIP), which enables not only voice services but also a range of multimedia services such as video, messaging, presence, file transfer, etc.
Within a wired data network, such as an Ethernet Local Area Network or the Internet, there is typically plenty of bandwidth to handle a VoIP communication session. However, in a network where bandwidth is relatively scarce, such as wireless cellular networks, there may be insufficient bandwidth and quality of service control to provide adequate service to implement a VoIP call. To address this issue, new standards such as the 3rd Generation Partnership Project (3GPP) IMS Centralized Services (ICS-TR 23.892) were introduced. ICS provides mechanisms such that all services, and service control, are based on IMS (IP Multimedia Subsystem) mechanisms and enablers, by combining SIP signaling over the wireless packet subsystem (PS) connection to the mobile, while the voice media bearer path is setup over the existing wireless circuit interface (Circuit subsystem—CS), avoiding the bandwidth intensive transport of voice over the IP PS connection. An ICS call can be seen as an hybrid VoIP call, combining packet-based signaling with circuit-based media.
Unfortunately, establishing a call using ICS mechanisms may take up to 9 or 10 seconds as SIP signaling first take place over the PS connection, followed by a voice call setup over CS. This call setup time is a relatively long amount of time, when compared to other signaling processes, which may lead to user dissatisfaction or complaints. Accordingly, it would be advantageous to provide a way to improve the process of establishing hybrid VoIP calls such as ICS calls into a wireless network.